My thoughts:Since species 1 and 2 are the least related, and 2 and 3 most related, the corrct diagrams should be:B,C,DIn fact, all three of the mentioned cladograms (B,C,D) show the very same thing.Am I mistaken or is it the author of the questions who says only B and D are correct?

As far as I know, they are not. In B and D there is one splitting between species 1 and 3 and 2 arised out of 3, which leads to 2 being closer related to 3 than to 1. This isn't the case for C. Here there is one splitting between 1 and 2 and 3 arised out of 2. This means that 3 is closer related to 2 than to 1.

Let's put it this way. In each case, there was firt organism A (in the very bottom). Then it split into 1 and B. Further B split into 2 and 3. And it doesn't matter how you switch the tree. All the parts are freely rotable.

Ok, I apologize if I confused the enquirer.I always thought that if I have a line straight through (without bends) that means that it is still the same species as it was when it split. But apparently I got that wrong.